Mobile devices such as laptops, tablets, personal digital assistants, cellular phones, smart phones, MP3 players, video gaming devices, navigation devices, etc. may be provided with a wide variety of wireless services. Examples of these services include but not limited to: Global System for Mobile Communications (GSM), Radio Frequency Identification (RFID), Distributed Control System (DCS), Personal Communications Service (PCS), Ultra Wide Band (UWB), Digital Video Broadcasting-Terrestrial/Handheld (DVB-T/H), Wireless Fidelity (WiFi), Blue Tooth (BT), World Interoperability for Microwave Access (WiMax), Long Term Evolution (LTE), Global Positioning System (GPS), etc. Correspondingly, the number of antennas in each device needs to be increased as the number of wireless services increases, thereby requiring antennas with small sizes and high performances. In particular, the antennas used for cellular communication are generally required to have high efficiency, signal quality, gain and other performance metrics as the operators dimension networks with respect to base stations according to those metrics; thus, there is a possibility that devices with low performances get excluded from even a minimal service depending on the dimensioned network.
One way to improve the quality of the link between the mobile device and the base station is to use an array of antennas on the mobile device so as to combine different beams to increase the signal strength in the direction of the base station. Such a technique, referred to as “beam forming,” is well known in theory to those skilled in the art. However, actual implementations for mobile devices or small systems have been difficult for the following two main reasons.
The first reason is that the space available for antennas in a mobile device or a small system is limited, as mentioned earlier. Even with the advancement of antenna technologies that achieve certain size reductions, the antenna dimensions are fundamentally related to the quarter wavelength of the frequency they are designed for. For example, in cellular low frequency bands (<1 GHz), such as GSM900 or GSM850, the quarter wavelength is about 9 cm in free space. Thus, putting even one antenna designed for cellular low frequency bands in a mobile device is already difficult due to the extremely small form factor, such as size and shape, of modern mobile devices. Needless to say, putting two or more low band antennas in a mobile device is a formidable undertaking without sacrificing some of the form factors.
The second reason is that the overall antenna system (including an array of antennas) should be able not only to perform beam forming but also to dynamically steer the direction of the high gain, or the peak of the beam, in the direction toward the base station as the relative position of the mobile device with respect to the base station changes. This technique, referred to as “beam steering,” requires an active circuitry to control phase shifts among radiation patterns of different antennas in the array, as well as a specific algorithm or program on the mobile device to control the circuitry, thereby leading to more complexities and real estate.